Sudden infant death syndrome (SIDS) is the sudden unexpected death of an infant under 1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation, including performance of a complete autopsy and review of the circumstances of death and the clinical history. SIDS is the most common cause of death in infants between the ages of 1 month and 1 year. SIDS is believed to be a natural cause of death, rather than due to accidents or homicide, yet its cause remains unknown. Because the cause of SIDS is unknown, SIDS parents have grief, which is complicated by guilt feelings that they may have done something to cause or contribute to the death. SIDS deaths have decreased with the institution of public health and public education measures, which emphasize having babies sleep on their backs. However, there is no known way to completely prevent SIDS.